This invention is related to the use of pH modifiers in the recovery of minerals by alkaline froth flotation process.
Froth flotation is the most widely used industrial process for the separation of finely divided minerals. The flotation process involves chemical treatment on the surface of a finely divided ore in a water pulp to create conditions favorable on the surface for the attachment of certain of the mineral particles to air bubbles. The air bubbles then carry the selected minerals to the surface of the pulp to form a stabilized froth, which is removed and recovered. The unattached materials remain submerged in the pulp and is either discarded or reprocessed. A wide variety of reagents, such as pH modifiers, collectors, frothers, and other bulk and surface modification reagents are used in froth flotation. Alkaline flotation with conditioning or flotation pH greater than 7 is widely used for beneficiation of oxide and semi-soluble salt minerals, such as apatite, barite, fluorite, scheelite, iron, kaolin. The most commonly used pH modifiers for alkaline flotation are caustic soda, soda ash, lime and ammonia. Some of the most used collectors, such as fatty acids and their derivatives, are thought to be effective collectors for oxidized mineral ores. However, a major challenge associated with the recovery of alkaline flotation is selectivity, thus the grade of the desired minerals in the concentrates. The limitation of effectiveness of the flotation process could be partially attributed to the pH modifier. Other problems associated with some pH modifiers are high consumption, foaming, and environmental concern. The invented pH modifier is intended to overcome the limitations of the traditional pH modifiers and at the same time to improve the alkaline flotation process as a promoter.
Phosphate rock in Florida is a typical sedimentary siliceous phosphate consisting of calcium phosphate in form of apatite together with clay, sand and other gangue minerals. The appropriately sized flotation feed with typical grade of 3 to 10% P2O5 is obtained through logging, washing, desliming and sizing. The feed in thick slurry is conditioned with pH modifier, fatty acids, fuel oil, and other co-collectors at pH 8.5 to 10. Sodium silicate sometimes is added as a silica depressant. The slurry is subsequently floated by conventional froth flotation routes. A rougher concentrate with typical grade of 20 to 30% P2O5 and 15-40% silica sand is acid-scrubbed, rinsed free of reagents, and subjected to a reverse cationic flotation to further remove the silica sand at pH 6.5 to 7.5. The final phosphate concentrate is produced with the double flotation process with typical grade ranging from 30 to 34% P2O5 with 10-4% sand (acid insoluble). Therefore, the alkaline pH modifier and silica depressant are only applied in the first stage, the rougher flotation.